...well, maybe that's a *slight* exaggeration.
The Great and Powerful Trixie, apparently laughed out of every town in Equestria by Bon Bon, Cherry Berry, Carrot Top, and a couple of other background ponies from Ponyville following her around, is forced to take up work on a rock farm, where she makes HUNDREDS OF BITS and becomes SUPER RICH. To get revenge for her newfound wealth, she spends it all on a cursed artifact.
Then she goes to Ponyville, where she challenges the local Sherriff (Twilight of course) to a duel at high noon, by zapping everypony in town with personalized body horror spells -- Rainbow Dash gets a giant wing, Rarity is forced to wear a hideous mexican outfit, Pinkie Pie has her mouth and nose removed. Apparently, magic duels in Equestria involve magician A doing a spell, that magician B has to match or counter. Trixie casts the 'eternal youth' spell, which is (just barely) too hard for Twilight, so Twilight admits defeat and leaves town, honest to her word.
HA HA JUST KIDDING, Trixie tosses her out bodily and then puts a forcefield around the town, imprisons the mayor, and enslaves everypony to perform increasingly *weird* and pointless tasks.
Banished to the swamps of Dagobah, Twilight apprentices under Zecora who apparently knows actual magic or something. She spends an indeterminate amount of time doing meditation exercises before Fluttershy is smuggled out of town to tell her that Trixie cheated by using an evil cursed amulet, and there's no possible way for her to win properly, so the whole training exercise was a complete waste of time.
Zecora, realizing that no plan survives contact with the viewers, imparts the strategy to defeat Trixie to Twilight in an impenetrable oracular rhyme. Basically, it boils down to 'cheat your pretty little tail off' with a dash of 'and trick Trixie into removing the stupid cursed amulet'.
Once purified of her evil, the now-sane Trixie immediately attempts to torture Rainbow Dash with electricity. Fortunately, her powers are weak again and she only manages to tickle her, so it's all in good fun, and everypony shares a laugh.
Later, in a truly cringe-inducing scene, Trixie proclaims herself the most apologetic unicorn in all of equestria, and runs off, presumably to earn another huge bag of bits breaking rocks.
The thing that struck me here is that AT NO POINT does anyone suggest anything resembling calling the cops or the army, aside from Twilight mentioning that Celestia is out of the country, so she has no one to call. EQUESTRIA DOES NOT HAVE A SYSTEM OF JUSTICE. It has local knights protecting the populace, and if they're defeated, well, the new boss takes over. Unless they're so awful that Celestia herself swings by to displace them, like when she made Twilight stop brainwashing everypony in Ponyville with her want-it-need-it spell.
I guess in other episodes we've seen that Canterlot (only) has the Royal Guard, and the Wonderbolts sometimes go around fighting monsters (badly) in their spare time. But... wow.
Overall... I liked most of this episode. It wasn't as bad as I was expecting. The scene at the end really was cringe-inducing, though, and there was no real point to any of it. Nopony learned anything -- 'don't use cursed amulets?' I guess maybe 'cheating is the path to victory' could be the aesop here.